Recently, in a radio environment such as a high-speed multimedia wireless communication system, a differentiated quality of service (QoS) has to be ensured as well as high-speed data rate.
An error correction scheme is used to secure communication reliability. Examples of the error correction scheme include a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, errors in received data are corrected by appending an extra error correction code to information bits. In the ARQ scheme, errors are corrected through data retransmission. Examples of the ARQ scheme include stop and wait (SAW), go-back-N (GBN), selective repeat (SR), etc. The FEC scheme has an advantage in that a time delay is not significant and no information is additionally exchanged between a transmitter and a receiver but also has a disadvantage in that system efficiency deteriorates in a good channel environment. The ARQ scheme has a disadvantage in that a time delay occurs and system efficiency deteriorates in a poor channel environment. To solve such disadvantages, a hybrid automatic repeat request (HARQ) scheme is proposed by combining the FEC scheme and the ARQ scheme. In the HARQ scheme, since retransmission is requested when the received data has unrecoverable errors, data transmission performance is improved.
The HARQ scheme can be classified into Type-I, Type-II, and Type-III. In the Type-I scheme, data is discarded when errors are detected, and retransmission of new data is requested. In the Type-II scheme, the error-detected data is not discarded and previous data is combined with retransmitted data. The retransmitted data and the previous data may have different code rates from each other. The Type-III scheme is different from the Type-II scheme in that the retransmitted data is a self-decodable code. That is, the retransmitted data can be decoded without having to be combined with the previous data.
In addition, the HARQ scheme can be classified into chase combining and incremental redundancy (IR). The chase combining is modification of the Type-I scheme. In the chase combining, the error-detected data is not discarded and is combined with the retransmitted data. The IR is the Type-II scheme or the Type-III scheme. This is because additional redundant information is incrementally transmitted when data is retransmitted in the Type-II scheme or the Type-III scheme. For identification purposes, the Type-II scheme may be referred to as full IR, and the Type-III scheme may be referred to as partial IR.
In the HARQ scheme, if no error is detected from received data, a receiver transmits an acknowledgement (ACK) signal as a response signal, and otherwise, if an error is detected from the received data, the receiver transmits a non-acknowledgement (NACK) signal. A transmitter retransmits data upon receiving the NACK signal. If the received data is unicast data which is transmitted to one specific user, error correction can be achieved according to the HARQ scheme. However, if the received data is multi-user data which is transmitted to users of a specific group or all users, there is no known method for transmitting the response signal.
Accordingly, there is a need for a method for transmitting a response signal by using a HARQ scheme when multi-user data is received.